Electrical contacts



3,8625 Patented Apr. 23, 1963 3,08,285 ELECTRICAL (IGNTACTS William Keitel, South Orange, N.J., assignor, by mesne assignments, to Engelhard Industries, Inc, Newark, N.J., a corporation of Delaware No Drawing. Filed Nov. 5, 1957, Ser. No. 694,528 6 Qiairns. (Cl. 29-199) The present invention relates to electrical contacts and, more specifically, to contact elements made substantially from silver.

It has been found that the properties of electrical silver contact elements can be greatly improved and their tendency to stick and weld can be reduced by treating the shaped contact element or the silver powder, which subsequently is shaped by well known compacting methods, with a solution of a heavy metal halide. The metallic silver reacts, in some cases at room temperature and in some cases upon heating, with the solution to form a thin coating of silver halide upon the surface of the shaped contact or the powder to be compacted, and simultaneously, the heavy metal of the halide is deposited in the form of extremely small, metallic particles finely dispersed in the layer of silver halide. This reaction occurs, as it was shown by numerous tests, with all heavy metal halides, which means all metals except the halides of the alkali metals and the earth alkali metal halides and may be attributed to the high afilnity of silver to the halide anion.

In accordance with the present invention, a solution of a heavy metal halide, preferably the chloride, is reacted with metallic silver thereby forming silver halide and simultaneously depositing finely divided metal onto the silver surface. This can be done by immersing the shaped contact element into the solution or, where the powder method is preferred, by treating at least a portion of the silver powder with the solution, followed by compacting which includes the known means of pelleting and sintering or hot extruding as well. In all cases pure silver or an admixture thereof, e.g. with metals or metal oxides or an alloy of silver, can be used.

Where the contact element is shaped previously, e.g. into the form of a rivet, and immersed in a solution of e.g. palladium chloride, the reaction proceeds until the whole surface is coated with a layer of silver chloride, which layer includes palladium metal in extremely fine dispersion. Upon completion of the coating, the reaction stops automatically, no more metallic silver being in contact with the solution.

The reacting silver surface area is much greater when silver powder or an admixture thereof is used and therefore the formation of silver chloride together with deposited finely divided metal will exceed the useful amount of about 6 percent, preferably 1 percent by weight. Consequently, powdered silver has to be present in such an excess that, after reaction, not more than about 6 percent by weight has been formed.

It may be assumed that each silver grain being in contact with halide actually reacts individually and forms a discontinuous coating which presumably consists of single particles dispersed upon its surface. As the reaction progresses the coating becomes more and more continuous until no more free silver surface is presented to the halide solution.

Another way to control the halide content consists in treating only a portion of the silver powder, followed by mixing with untreated powder in such a proportion that the desired content of halide in the powder mixture is obtained. An excess of silver chloride was found to cause exudations during the following process of compacting or during performance of the finished contact.

The preferred halides according to the invention are the chlorides and best results were obtained with chlorides of rhodium, ruthenium, gold, copper and especially palladium. However, silver powder treated with copper chloride oxidized by heating in air (1200 F.) and compacted into contact elements performs especially well with heavy currents as shown in the following Example 3, and it can be assumed that the presence of extremely finely divided particles of metal or metal oxides included in the layer of silver halide contributes to a large extent to decrease the sticking tendency of the finished contact, since the method according to the invention results in an extremely fine and uniform dispersion which cannot be obtained by mechanical processes.

Example 1.-An aqueous solution of palladium chloride was prepared by dissolving 1 gram of palladium chloride in one liter of distilled water. Fine silver rivets of the commercial type of /s diameter were immersed in the solution. The reaction stopped after each rivet had a strong film of silver chloride and metallic palladium formed on the surface thereof.

When tested, after drying, at 30 amperes, 115 volts A.C., the rivets showed a stick frequency of 3 sticks per 120,000 makes and breaks. Similar rivets, without being treated with halide solution and under the same conditions, produced more than 200 sticks. The millivolt drop was found to be about 3 millivolts across the contact as compared to about 8 before the treatment with palladium chloride solution.

Example 2.--Silver contact elements containing 10% cadmium oxide were treated with the palladium chloride solution of Example 1, dried and tested at 300 amperes and 115 volts AC. The normal sticking frequency of about 3 per 200 operations was reduced to l per 200 operations.

Example 3.30 grams of silver powder were heated with a solution of 2 grams of copper chloride in ml. distilled water on a steam bath. The silver powder turned copper-red and acquired at the same time a coating of silver chloride while the solution became colorless. The powder was dried, furnaced in air, yielding a black powder, as the copper was transformed into its oxide, and compacted into pellets. When tested, no sticks occurred during 300 operations at 300 amperes and volts AC.

The following table illustrates the results of tests made with rivets of fine silver treated with other metal chloride solutions than mentioned in the foregoing examples and as compared to untreated silver rivets. These tests were executed with 6 pairs of each contact rivet for 40,000 operations at 30 amperes resistance load and 115 AC.

Average Mlllivolt sticks drop at 10 ampercs Fine silven 49 4-12 Gold chloride- 25 5-11 Rhodium chloride 19 5-15 Ruthenium chloride... 18 3-8 silver halide being' not more than 6% by weight of the silver.

2. An electrical contact element as set forth in claim 1 made by reacting a heavy metal halide with silver thereby to produce the silver halide with particles of th heavy metal dispersed therein.

3. An electrical contact element as set forth in claim 1 in which the heavy metal is selected from the group consisting of palladium, rhodium, ruthenium, gold and copper.

4. An electrical contact element as set forth in claim 1 in which the silver halide is silver chloride.

5. An electrical contact element as set forth in claim 1 in which the silver halide is silver chloride and the heavy metal is palladium.

6. An electrical contact element as set forth in claim 1 in which the silver halide is silver chloride and the heavy metal is palladium and which is made by reacting palladium chloride with silver thereby to produce silver chloride with particles of palladium dispersed therein.

References Cited in the file of this patent UNITED STATES PATENTS Smith July 28, 1914 Pahrenwald Aug. 7, 1917 Pfanstiehl Sept. 9, 1919 Ehlers Nov. 8, 1927 Hensel Nov. 21, 1939 Slepian Aug. 19, 1941 Reeve Dec. 1, 1942 Larsen May 18, 1943 Wagenhals June 29, 1943 Alexander June 20, 1944 Constock Dec. 19, 1944 Swinehart Aug. 5, 1947 Richardson Oct. 23, 1951 Underwood May 21, 1957 Egan Nov. 5, 1957 Hoyer Jan. 7, 1958 Streicher May 23, 1961 

1. AN ELECTRICAL CONTACT ELEMENT CONSISTING ESSENTIALLY OF SILVER, A COATING OF A SILVER HALIDE ON AT LEAST A PORTION OF THE SILVER AND FINELY DIVIDED PARTICLES OF HEAVY METAL DISPERSED IN THE SILVER HALIDE COATING, THE AMOUNT OF SILVER HALIDE BEING NOT MORE THAN 6% BY WEIGHT OF THE SILVER. 